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Патент USA US2406045

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Aug. 20, 1946.
2,406,045
B. E. STEVENS
INDUCTANCE DEVICE
Filed May 30, 1944
3.3
m.
2 Sheets-Sheet l
M
m/ve/vrop
_
B. E. STEVE/V5
BY
A TTORNE V
‘ Aug. '20, 1946.
B, E, STEVENS
' >
2,406,045
INDUCTANCE DEVICE
‘Fiied May 50, v1944
,
M‘
2 Sheets-Sheet 2
\.,/v
FIG’. 6
FIG. 9
lA/VENTOF?
51 E STEVE/V5
By
Patented Aug. 20, 1946
2,406,045
UNITED STATES PATENT OFFICE
2,406,045
INDUCTANCE DEVICE
Bruce E. Stevens, Demarest, N. J., assignor to Bell
Telephone Laboratories, Incorporated, New
York, N. Y., a corporation of New York
Application May 30, 1944, Serial No. 538,065
9 Claims.
(Cl. 175——356)
1
This invention relates to an inductance device
or apparatus such as power transformers and its
object is to reduce the stray magnetic flux from
such apparatus.
Although the invention is of general applica
tion to stationary induction apparatus it will be
illustrated as applied to a power transformer hav
ing a shell-type core with the usual primary and
secondary windings surrounding a leg of the core.
As is well understood in the art there is a certain
amount of stray magnetic flux from such a core
2
gether and so connected to the auxiliary winding
proper that the voltages developed in the bolts
by reason of the ?ux traversing the core path be
tween each bolt and the adjacent outer edge of
the core are additive and are also additive with
respect to the voltage developed in the turns of
the auxiliary winding by the stray ?eld whereby
the ?eld set up by the flow of current in the aux
iliary winding will be in the proper direction to
oppose and tend to neutralize the stray ?eld.
The invention will be better understood by ref
which is generally objectionable in that it may
erence to the following detailed description taken
be picked up by adjacent apparatus and gives
in connection with the accompanying drawings
rise to disturbing potentials in a signaling cir
in which:
cuit.
15
Fig. 1 is a perspective view of an unpotted shell
In accordance with this invention the stray
type transformer in which the stray ?eld is re
magnetic ?ux from such a device is substantially
duced by the auxiliary winding of this invention;
reduced by the use of a closed circuit auxiliary
Fig. 2 is a schematic view of the transformer of
winding of one or more turns which surrounds
Fig. 1 in which the electromotive force developed
the core and the main winding and is coaxial 20
in the auxiliary winding is obtained from two of
with the main winding and which is so arranged
the clamping core bolts;
as to have developed therein a current of the
Fig. 3 is a top view of Fig. 1;
proper magnitude, wave form and phase to set up
Fig. 4 is an enlarged plan view of a corner por
a ?eld which opposes the external ?eld of the
tion of the laminated core of Fig. 1;
transformer. The preferred source of electro 25
Fig. 5 is a sectional view of the laminated core
motive force for this auxiliary winding is ob
portion of Fig. 4 taken along the line 5-5 of
tained by having a portion of this auxiliary wind
Fig. 4;
ing enclosed only by that portion of the ?ux path
Fig, 6 is a modi?cation of the transformer of
in the core which is rich in harmonics of the
Fig. l in which only one core bolt is utilized as
fundamental frequency of the stray ?eld so that 30 part
of the auxiliary winding;
the opposing ?eld set up by the auxiliary winding
Fig, '7 is similar to Fig. 6 except that four core
will tend to neutralize not only the fundamental
bolts are included as parts of the auxiliary wind
frequency but the harmonics of the stray ?eld.
111g;
In a shell-type core having its main winding con
Fig. 8 illustrates an alternative arrangement
nected to a GO-cycle source of current to produce
35 utilizing a different portion of the core structure
a magnetic ?ux in the core, one portion of the
for inducing current in the auxiliary winding,
magnetic path in the core which will have a ?ux
and
rich in harmonics is that portion of the core near
an outer corner thereof where the flux path is of
Fig. 9 illustrates the transformer of Fig. 1 en
higher reluctance. In the preferred embodiment 40
of the invention a portion of the auxiliary wind
ing is made to pass through an opening in the
closed in a suitable case.
Referring more particularly to Fig. l, the trans
former disclosed is of the shell-type comprising
a core l0 made up of a plurality of laminations
core near an outer corner thereof and in a direc
of suitable magnetic material. The main wind
tion perpendicular to the plane traversed by the
ing II may comprise superimposed primary and
core ?ux so that the auxiliary Winding is enclosed 45 secondary windings which are wound around the
by the ?ux passing between said opening and the
middle leg of the core in the usual manner. The
adjacent outer corner of the core. In the manu
laminations of the core are held together by bolts
facture of such power transformers, the core is
I2, I3, [4 and I5 and cooperating nuts. Each of
usually made up of laminations held together by
the
bolts I2 and I 3, is suitably insulated from the
clamping bolts. In practicing the present inven 50
core as shown, for example, in Fig, 5 where the
tion one or more of these bolts may be placed at
bolt I3 is insulated from the core Ill by means of
the corners of the core structures and suitably
the insulating sleeve I 6 and the insulating wash
insulated from the core whereby these bolts may
ers I1 and I8. From Fig. 4 it will be apparent
constitute portions of the auxiliary winding above
described. Such bolts should be so connected to
that bolt I 3, for a purpose which will be described
55
later, is located substantially closer to the outer
2,406,045
3
Due to the particular location of the core bolts
corner it of the core than to the inner corner
29 thereof. Bolt 52 at another corner of the core
structure is insulated from the core in a similar
I2 and 93 at the corners of the shell-type core ID,
the electro-motive force developed thereby in aux
iliary winding ii is also rich in harmonics of the
manner and placed in the same relative positions
as bolt iii. In Fig. l the other clamping bolts M
fundamental frequency of the current supplied
from the primary winding 25.
and it need not be insulated from the core.
The core iii and the main windings l l are sur
rounded by
winding
The following data show that the electromotive
force induced in core bolts l2 and I3 is rich in
harmonics of the fundamental frequency. Let a
single layer multiturn auxiliary
which is wound coaxially with the
represent the core section lying between the core
window and bolt l3; 1) the core section lying be
main winding. As shown in Figs. 1 and 2, one
terminal 22 of auxiliary winding 2i is electrically
tween bolt i3 and the adjacent outer corner of
the core; and c the core section at the point
marked 0 in
2. The following values are
connected to the front end of bolt 22 while the
other terminal 23 of winding 2! is electrically
connected to the front end of bolt
rFhe rear
the component voltages induced in one turn on
ends of bolts l2 and i3 are electrically connected 15 open circuit enclosing sections a, b and 0 respec
by a strap 25. The
2d and the turns of
tively, with respect to the flux density in the cen
auxiliary winding 2i are covered with a suit
ter
leg of the transformer:
able insulating material. Auxiliary winding 2!
with the bolts l2 and i3 and strap 2-’! therefore
Millivolts in one turn
constitute a closed circuit in which an electro 20
motive force will be induced by reason of the fact
that a portion of the auxiliary winding is en
Center leg ?ux density
Semen
closed by that portion of the ?ux path in core ill
which passe between bolt l3 and the adjacent
corner edge of the core and between bolt l2 and 25
the adjacent corner edge of the core.
Referring more particularly to the schematic
View of the transformer shown in Fig. 2, only the
primary or magnetizing winding 25 is disclosed,
while the superimposed secondary winding is
-
lines per sq. Ill.
60
180
300
C. P. S.
C. P. S.
C. P. S
465
425
385
78
60
45
535
57
44
34
16
21
14. 5
9. 5
5. 5
7.0
4. 0
2. 5
10
485
20
7. 4
a
b
c )l
30 56 000
omitted to simplify the drawings. Assume for
the moment that the terminals 32 and 33 of pri—
mary winding 25 are connected to a GO-cycle
power source and that for a given half cycle of
the current therefrom the flux path in core ill
430
38
25
20
2. 4
Regarding phase relations, if the core bolt
i3 is considered merely as a secondary winding
of the transformer, the voltage induced in core
bolt vl3 would be 180 degrees out-of-phase with
is indicated by the dotted lines 3% to 3? traveling
the voltage applied to the magnetizing winding
in directions indicated by the arrows thereon.
25 and 90 degrees out-oi-phase with the external
While most of the flux (Pa will take the paths in
?eld.
To obtain from the auxiliary winding 2|
dicated by lines 353 and St, a portion of the flux
<I>b will take the paths indicated by lines 35 and 40 a ?eld which is 180 degrees out-of-phase with
respect to the external ?eld of the transformer,
37. Bolts S22 and 51-5 are within tile path of the
it is necessary to provide sufficient reactance in
flux @b which induces a voltage in them so that a
the close circuit comprising winding H. The
current will flow if they are connected in a closed
electrical connection or” core bolts l2 and £3 with
circuit. As shown in Fig. 2, the two bolts l2 and
the
multiturn winding 2! provides this react
45
iii are electrically connected in a closed circuit
ance. A core bolt, such as bolt i3, is not well
including auxiliary winding ‘Eli and strap 22 in
coupled with the primary winding 25 and can
such a manner that the voltages developed in the
be
considered in series with a leakage reactance.
two bolts are additive, the direction of current
By drawing sufficient current from the core bolts
flow in the two bolts being indicated by the solid
line arrows 33 and 39 of Fig. 2 for the flux di 50 52 and i3 this leakage reactance is effective in
rection in the core indicated in the same ?gure
with due consideration of time-phase relations.
producing the proper phase relation, together
with that reactance provided by the multiturn
winding 2!. To obtain a large current only a
few turns of heavy wire are used in the auxiliary
in winding 2i by reason of the stray field from 55 winding 2! so that it has a low resistance.
In one particular embodiment where auxiliary
core ill is additive to the voltages induced in bolts
rf‘he turns of winding ii are wound around core
if? in such a direction that the voltage induced
l2 and i3.
_
rE‘he magnetizing current supplied the trans
former, Fig. 2, by primary winding 25 may be
largely distorted depending on the flux density
at which the core is operated. This distortion
arises mainly from the hysteresis in the mag
netic circuit. Because of this distortion the stray
field is rich in harmonics of the fundamental
frequency of the current supplied to primary
winding 25.
It is well known that the magnetizing current
of a transformer increases rapidly with the in
crease of ?ux density in the core and that the
harmonics increase at a greater rate than the
fundamental. Since the external or stray ?eld
of the transformer is a function of the magnetiz
ing current, it is essential that the current in
auxiliary winding 2i change in the same manner
as the magnetizing current of the transformer.
winding 21 comprised eight turns of heavy cop
per wire uniformly spaced over substantially the
entire core structure iii, it was found by measure
ment that the current in winding 2| was approx
imately 5 amperes.
It has been found in utilizing one embodiment
of this invention that the stray ?eld of a shell
type transformer using no metallic casing for
the transformer will have its external ?eld re
duced by an amount of 10 to 14 decibels for the
fundamental frequency and with a decibel loss
almost as large for the harmonics when an aux
iliary winding of the type illustrated in Fig, l is
employed.
However, this invention may also be advan
tageously employed for reducing the external ?eld
of transformers that are ordinarily enclosed in a
metallic case. For example, in Fig, 9 a shell
’ type transformer of Fig. 1 is shown enclosed in a
2,406,045
5
suitable casing 40 of magnetic material such as
steel or Mumetal.
The following measurements indicate the ex
tent to which the external ?eld may be reduced
by the employment of the auxiliary winding of
this invention. As indicated, one set of measure
ments was taken for a transformer of the type
disclosed in Fig. 1 without any auxiliary wind
ing but with an enclosing casing of steel. An
other set of measurements gives the external ?eld
for a transformer of the type in Fig. 1 including
an auxiliary winding 2| electrically connected in
circuit with two of the core bolts as indicated
in that ?gure and with the transformer enclosed
in the same steel case as for the ?rst set of
measurements. For the third set of measure
ments the conditions are the same as for the
second set except that the transformer case was
of Mumetal instead of steel. The voltage values
given in the following tables are millivolts pick
up with a small search coil six inches from each
side of the transformer indicated:
6
connected to the opposite ends of core bolt 44
whereby bolt 44 serves the same function as core
bolt l3 to produce in auxiliary winding 42 a cur
rent of the proper magnitude, phase and wave
form to reduce the external ?eld of the trans
former. In Fig. '7 the laminated core 45 is sur
rounded by a multiturn auxiliary winding 46
wound eoaxially with the magnetizing winding 41
and the four core bolts 48, 49. 5.0 and 5| are
electrically connected in a closed circuit compris
ing auxiliary winding 46 in such a manner that
the electromotive .forces induced in the four core
bolts are additive and so connected to the aux
iliary winding 45 that the current produced
thereby in said winding is of the proper magni
tude, phase and wave form to produce a substan
tial reduction in the stray ?eld of the transformer.
Bolts 44, 48, 49, '50 and 5| are insulated from the
core in the same manner as described for bolt
l3 of Fig. 1.
A further alternative form of the invention is
disclosed in Fig. 8 where the core 56 is of the shell
type having a magnetizing winding 51 wound
Table A-where the transformer has no auxiliary
around the center leg of the core. A multi-turn
winding and is enclosed in a steel case
25 single layer auxiliary winding 58 surrounds core
56 and is wound eoaxially with the magnetizing
Frequency,
Bottom Broad Narrow
winding 51. The core of Fig. 8 differs from the
O. P. S.
side
side
side
cores of the earlier ?gures in that the clamping
bolts 59 and 60 for the core laminations also
15. 0
7. 7
6. 7
l1. 0
5. 4
4. 6 30 hold in place against the core structure a strip
2. 8
1. 5
l. 2
6| of magnetic material. One portion 62 of strip
BI is located directly above one of the windows
Table B-where the transformer is enclosed in
in the core structure while another portion 63
the same steel case above-mentioned but the
of strip 81 is located directly above the other
transformer is provided with the auxiliary
window in the core structure; both portions 62
winding of Fig. 1
and 63 being spaced laterally from the core struc
ture. The central portion 64 of strip G! is in
Frequency,
contact with the main core directly above the
Bottom
Broad Narrow
side
0. P. S.
side
side
center leg of the transformer core. The flux
traversing sections 62 and 63 of strip 6| will be
rich in harmonics of the fundamental frequency
of the stray ?eld for the same reasons as the
flux traversing section b of the core of Fig. 2. As
Table C-where the transformer is enclosed in a
Mumetal case and is provided with the auxil
iarg winding of Fig. 1
Frequency,
Bottom
Broad
Narrow
O. P. S.
side
side
side
0. 14
0. 05
0.06
. 13
. 01
. 08
. 11
. O3
. 04
shown in Fig. 8, the auxiliary winding 58 includes
one or more turns wound around strip- portion
62 and one or more turns wound around strip
portion 63. Assuming the direction of the flux in
core 56 is the same as that indicated by the dotted
lines in Fig. 2, the direction the turns 65 are
50 wound around strip 62 and the direction the turns
66 are wound around strip 63 and the direction
the main portion of winding 58 is wound around
core 56 are such that the electromotive force
induced in turns 65 is additive with respect to
It is to be understood that the number of core 55 the voltage induced in turns 65 and the sum of
these two voltages is additive to the voltage de
bolts electrically connected in the closed circuit
veloped in the main portion of winding 58 due to
including the auxiliary winding depends upon the
?eld strength desired from the auxiliary winding,
the external ?eld of the transformer. The ar
rangement of Fig. 8 will, therefore, produce a sub
In Fig. 1 two of the core bolts I2 and I3 are
electrically connected as part of the auxiliary 00 stantial reduction in the external ?eld of the
transformer in the same manner and to the same
winding 2| while in the modi?cation illustrated
in Fig. 6 only one core bolt is included in circuit
extent as is secured by the earlier described em
with the auxiliary Winding and in Fig. '7 four
of the core bolts are connected in circuit with
bodiments of the invention.
It is also to be understood that this invention
the auxiliary winding.
65 may possess still other embodiments commen
surate with the scope of the appended claims.
A detailed description of the embodiments il
What is claimed is:
lustrated in Figs. 6 and 7 is believed unnecessary
since these ?gures are identical with the embodi
1. An inductance device comprising a magnetic
ment of Fig. 2 except for the number of core bolts
core, a main winding wound only on one portion
electrically connected in the closed circuit com 70 of said core and adapted to be traversed by al
prising the auxiliary winding. In Fig. 6 the lam
ternating current of a de?nite frequency, said
inated core 4| is surrounded by multiturn aux
core having such a con?guration that a second
iliary winding 42 which is wound eoaxially with
portion of said core external to said winding is
the main magnetizing winding 43 and the two
traversed by a‘?ux rich in harmonics of the ‘fun
terminals of auxiliary winding 42 are electrically 75 damenta1
frequency of said current, and means
‘2,406,045
7
for reducing the stray ?eld from said core, said
‘means comprising a closed circuit of negligible re
sistance comprising an auxiliary winding sur
rounding said core and said main winding and co
axial with said main winding, a portion of said
auxiliary winding being enclosed only by said
second core portion, said auxiliary winding por
tion and the remainder of said auxiliary winding
8
tral portion, clamping bolts for holding said lami
nations together, at least one of said bolts being
insulated from said laminations and passing
through said laminations near an outer corner
of said core, an auxiliary winding embracing said
core and with the main portion of said auxiliary
winding wound coaxially with said main Winding,
and a closed electrical circuit including said aux
iliary winding and said one bolt connected in
being so connected that the current ?ow in said
auxiliary winding produced by the flux travers 10 series.
6. An inductance device comprising a substan
ing said second core portion produces a magnetic
tially rectangular-shaped core, a main winding
?eld opposed to the stray ?eld of said device.
on one limb of said core, a closed electrical cir
2. An inductance device comprising a magnetic
cuit of negligible resistance comprising an aux~
core, a main winding wound on only one portion
iliary winding wound externally around said core
15
of said core and adapted to be traversed by alter
and wound coaxially with said main winding, a
nating current of a de?nite frequenc‘ , said core
having such a con?guration that a second por
tion of said core external'to said main winding
is traversed by flux in which harmonics are pres
ent with respect to the fundamental frequency
in ratios of substantially the same order of mag
nitude as in the stray ?eld of said device, and
means for reducing the stray ?eld from said
core, said means comprising a closed circuit of
auxiliary 25
negligible resistance comprising an
winding surrounding said core and said main
winding and coaxial with said main winding, a
portion of said auxiliary winding being enclosed
only by said second core portion, said auxiliary
winding portion and the remainder of said auxil
iary winding being so connected that the current
flow in said auxiliary winding produced by the
‘ flux traversing said second core portion produces
a magnetic ?eld which is substantially 180 degrees
out-of-phase with respect to the stray ?eld.
3. An inductance device comprising a substan
tially rectangular-shaped core of magnetic ma
terial de?ning two closed magnetic paths hav
ing a common path through a central portion of
said core, a main winding on said central portion, m.
and means for reducing the stray ?eld from said
device, said means comprising a closed circuit
multiturn auxiliary winding embracing said core
and with the main portion of said auxiliary wind
ing' wound coaxially with said main winding, said
auxiliary winding having a portion threading
through said core near an outer corner thereof in
portion of said auxiliary winding passing through
a portion of said core external to said main wind
ing and in a direction perpendicular to the plane
of the ?ux traversing said core, said auxiliary
winding portion being located closely adjacent
an external corner of said core such that the dis
tance between said external corner and said aux
iliary winding portion is considerably less than
the distance between said auxiliary winding por—
tion and the adjacent inner corner of said core.
'7. An inductance device comprising a substan
tially rectangular-shaped core of laminations of
magnetic material, clamping bolts for holding
said laminations together, a main winding on one
limb of said core, an auxiliary winding embrac
ing the entire core structure and wound coaxial
ly with said main winding, one of said bolts pass
ing through a portion of said core external to
said main winding and being closely adjacent an
external corner of said core such that the dis
tance between said external corner and said bolt
is considerably less than the distance between
said bolt and the adjacent inner corner of said
core, said one bolt being insulated from said
laminations, and a closed circuit including said
auxiliary winding and said one bolt connected in
series.
8. An inductance device comprising a substan
tially rectangular-shaped core of laminations of
magnetic material de?ning two closed magnetic
paths having a common path through a central
portion of said core, a main winding on said cen
a direction substantially perpendicular to the
tral portion, clamping bolts passing through said
plane of the flux through said core.
laminations for holding said laminations together,
Ll. An inductance device comprising a substan 50 said bolts being electrically insulated from said
tially rectangular-shaped core of magnetic ma
laminations, one of said bolts being located close~
terial de?ning two closed magnetic paths having
a common path through a central portion of said
core, a main winding on said central portion, and
means for reducing the stray ?eld from said de“
vice, said means comprising a closed circuit multi
turn auxiliary winding embracing said core and
with the main portion of said auxiliary winding
wound coaxially with said main winding, said
auxiliary winding having a portion threading
through said core near an outer corner thereof
in a direction substantially perpendicular to the
plane of the ?ux through said core, the direc
tion the turns of said auxiliary winding are
wound on said core being such that the electro
motive force developed in the portion of said aux
iliary winding threaded through the core produces
a current in said auxiliary winding which sets
up a magnetic ?eld opposing the stray ?eld of
ly adjacent one external corner of said core such
that the distance between said one external cor
ner and said One bolt is considerably less than the
distance between said one bolt and the adjacent
inner corner of said core, a second of said bolts
being located closely adjacent a second external
corner of said core such that the distance between
said second external corner and said second bolt
is considerably less than the distance between said
second bolt and the adjacent inner corner of
said core, a single layer multiturn auxiliary winding surrounding the entire core structure and
wound coaxially with said main winding, the axial
length of said auxiliary winding being at least
equal to the axial length of said main winding,
and a closed circuit of negligible resistance com
prising said ?rst bolt, said second bolt and said
auxiliary winding connected in series, said first
said device.
bolt and said second bolt being so connected to
5. An inductance device comprising a substan
said auxiliary winding that the electromotive
tially rectangular-shaped core of laminations of
forces induced in said bolts are additive to pro
magnetic material de?ning two closed magnetic
duce a current flow through said auxiliary windpaths having a common path through a central
ing in the same direction as the current devel
portion of said core,_a main winding on said cen' "
9
2,406,045
10
oped in said auxiliary winding due to the stray
said current, and means for reducing the stray
?eld of said device.
9. An inductance device comprising a mag
?eld from said core, said means comprising a
closed circuit of negligible resistance comprising
an auxiliary winding surrounding said core and
said main winding and coaxial with said main
winding, a portion of said auxiliary winding
netic core, a main winding wound on one section
of said core and adapted to be traversed by alter
nating current of a de?nite frequency, said core
external to said winding having a portion of in
threading through said aperture and enclosed
only by said one ?ux path, said auxiliary wind
ing portion and the remainder of said auxiliary
winding being so connected that the current ?ow
in said auxiliary winding caused by the flux trav
creased cross-sectional area as compared with
adjacent sections of said core, said core portion
having an aperture dividing the ?ux traversing
said core portion into two paths, one path hav
ing a higher reluctance than the other path
whereby said one path is traversed by flux rich
in harmonics of the fundamental frequency of
ersing said one ?ux path produces a magnetic
?eld opposed to the stray ?eld of said device.
BRUCE E. STEVENS.
15
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